Preheat oven to 350F.
Cream sugar and butter. Add flour, baking powder and eggs and beat well.
Spoon batter into 9″ spring form pan. Arrange plum halves face down in batter. Sprinkle lightly with sugar and lemon juice, depending on the sweetness of the fruit. Sprinkle on cinnamon.
Bake at 350F for 1 hour. Batter will rise and cover plums.
Remove and cool, refrigerate or freeze if desired. Or cool to lukewarm and serve with vanilla ice cream or whipped cream.
To serve frozen tortes, defrost and reheat briefly at 300F.